Poly intake and carb

[gwintx]

I have a 65 Coronet with the 318 Poly. It has the stock 2 BBL carb and manifold. I’ve found a Weiand 7503 dual plane manifold for it and need to decide on a carb. We have several carbs laying around already so I’d like to rebuild one of those, rather than buy one. The two most likely candidates are a Carter 9635SA Competition Series and a Holley 80670 (vacuum secondary). I’m afraid the Holley is too big at 670 CFM, so I was leaning towards the Carter (625 CFM). Is 625 CFM still too much for this engine? I’m pretty sure it’s completely stock since it still has the stock carb, intake and exhaust.

If the Carter will work, I have a couple questions:

First, it’s missing some of the linkage on the throttle linkage side. It was an aftermarket carb, so it has the universal (Chevy?) linkage. The throttle linkage is there, but the rest is not. I wasn’t sure what the missing bits were for, but searching the web, it seems it’s either a secondary lockout or fast idle linkage, or both. My understanding is that the secondary lockout is just to prevent the secondaries from opening while the choke is on. Doesn’t seem like I absolutely need that since I won’t be flooring it while it’s cold. What about fast idle? If I tune the engine well, do I really need that? There’s a pic below to show what’s missing.

My next question, assuming I use the carb, is what jets, metering rods and metering rod piston springs would you recommend for a stock 318 Poly? This carb was on a 440 so it’s possible it was tuned to that engine and those pieces were changed out.

 

[RustyRatRod]

The Holley is not too big.

 

[DWinTX]

Rusty, why do you think the Holley is not too big? All of the standard CFM calculations say a stock motor with 318 cubic inches and a max RPM of 6500 (I have no idea if that's right for this motor but it is a small block with solid lifters) needs about 600 CFM. Is it because these poly heads flow better stock than wedge style heads? Not doubting you, just interested in being educated by people smarter than me on this stuff.

I'm still interested in what a good stating setup on the Carter would be for this motor. Since we already have them, we might try both to see which one works better. Plus the Carter looks a little more "Mopar-Like" since so many were used as OE equipment.

FYI, reason I'm so interested is that I'm the OP's dad and am helping him with this project.

 

[RustyRatRod]

Those formulas are for max CFM only. They take no consideration as to what type carburetor it is. The Holley 670 is a vacuum secondary carburetor. All you'll need to do is tune the primary side to the engine and maybe put a different secondary spring in. You might not need to do that. Vacuum secondary carburetors only flow what an engine demands. That's why they are so versatile. Chrysler knew it, too. That's why you can take a Thermoquad off a 440, slam it on a 318 and do almost nothing for tuning. The carbureter's rating is 670 CFM maximum. The little 318 will probably flow that, but at 7K RPM. I would use the 670, because it will have a better booster signal and better throttle response when it's dialed in.

Check this site out.

http://www.1962to1965mopar.ornocar.com/poly318.html

There's some good stuff about Polys there. You know, a Mopar 4" crank will drop right in. 402 screamin cubes of Poly.

 

[DWinTX]

OK, thanks for the explanation. I have read that poly page on the 62 to 65 site, as well as the article Gary P. did for Mopar Muscle. That 402 stroker looks awesome. I would be willing to bet we'll do that someday with this car. Right now though, my son wants to use it as a daily driver while he's in college. So most of our initial work is to rebuild the suspension, add some 3 point seat belts and do a disk brake conversion to make it safe. I ran across the intake for sale and since they are discontinued I thought I grab it. Since we already have the carbs we figure we'd throw them on for a little extra punch.

 

[RustyRatRod]

I swear I think that Holley will do you a better job. Truthfully, I am not a fan of the Edelcrap/Carter style carburetors.....however, I am not biased enough that I would not tell you if I thought the Eddy would do a better job. I just don't think it will.

 

[lewtot184]

personally, i like both holley and carter carbs; but they can be different animals doing the same thing. i don't get lost in the cfm ratings. most of them are over rated and i don't believe in picking a carb by cfm only. if you you think in terms of venturi area the holley is actually smaller. it gets it's extra flow from a better shaped entry. both carbs have velocity controlled secondaries so neither should be torque killers. the manifold is a torque killer. all weiand single four and dual fours that i've seen are single plane. either carb will work. if you use the carter just go back to the factory baseline jetting. i do think the holley will make a little more mid-range torque due to its smaller venturi area and the secondaries opening rate can be tuned.

 

[DWinTX]

Alright, you guys convinced me to give the Holley a try.

One benefit is that I won't have to rebuild it. It's almost new.